The present invention relates generally to a shielded electrical connector for terminating a cable assembly of multi-pair shielded cable used for transmitting high frequency data signals, and relates in particular to an auto-latching sliding contact mechanism that matches the impedance between two connectors.
Several problems become evident in data transmission networks when data is transmitted at high frequency over multi-pair shielded cable. In particular, at high transmission rates each wiring circuit itself both transmits and receives electromagnetic signals, so that the signals flowing through one circuit or wire pair may couple with the signals flowing through another circuit. The unintended electromagnetic coupling of signals between different pairs of conductors of different electrical circuits is called cross-talk, and is a source of interference that often adversely affects the processing of these signals.
Another problem occurs at the point of interconnection between a male connector and a female connector. Contact is made automatically at the interface between the two connectors when the male connector is introduced into the female connector. Such contact must both ensure electrical continuity and provide stability to prevent the two connectors from being easily separated. A mechanism for providing stable contact is described in European patent application EP 0.634.817, wherein the contacts of both connectors are identical and have an elongated base portion and a reversely directed cantilevered spring portion separated by a rounded bump. When the two connectors are interconnected, the rounded bump of the male connector comes in behind the other bump due to the lowering of the two cantilevered spring portions, resulting in an auto-latching electrical contact between the two connectors.
Unfortunately, even though such an auto-latching contact has the advantage of requiring no other mechanical locking, it also has an important drawback when used to transmit data signals at a very high frequency due to the geometrical discontinuity at the point of contact. Indeed, at this point there are at least two layers of contact blades, which results in a difference of thickness across the point of contact. Such a difference causes a discontinuity in the common mode impedance that is detrimental when the frequency is higher than 600 MHz, and especially as the frequency approaches 1200 MHz.
Accordingly, an object of the invention is to provide an auto-latching sliding contact mechanism without discontinuity of the common mode impedance across the point of contact.
The invention includes a connector designed to be interconnected to another connector of the same type to connect cables containing twisted pair for the transmission of very-high-frequency differential data signals. The conductors of the pair are connected in a connection block by means of Insulation Displacement Contacts (IDC) to contact blades that include an auto-latching mechanism adapted to ensure contact in a interface block with the corresponding contact blades of the other connector. Each of the contact blades has a constant thickness, and has an initial width (W) in its rectilinear part and a narrower second width (Wc) in the portion where the contact is made with the corresponding portion of the contact blade of the other connector, such that the common mode impedance is equal to:       Zc    =                  60                              ϵ            ⁢                          xe2x80x83                        ⁢            r                              ⁢              Ln        ⁡                  (                                    1.9              ⁢              B                                                      0.8                ⁢                W                            +              T                                )                      ,
where Ln stands for neperian logarithm, and B=2H+T, where H is the distance between the middle point of the base of the blade and the wall of the cavity, and is the same in the rectilinear part and in the portion where the contact takes place when Wc=Wxe2x88x921.25T.